New types of lightweight and ultra-lightweight aircraft are being developed for recreational use, use by novice pilots, and/or for use in new flying environments (e.g., they can take off and land from a backyard). In some of these aircraft, the rotors have no shield or blade and are therefore exposed. New techniques to detect a rotor strike and reduce the rotor's force in response to detection of a rotor strike would be desirable. Although strike detection techniques may exist for other applications, it would be desirable if techniques were lightweight, low cost, and/or better suited to the various needs and/or design considerations of an aircraft.